Metallurgical flux and method of producing it



Patented Nov. 5,1940

UNITED STATES IPATENT OFFICE METAILURGICAL FLUX AND DIETHOD h PRODUCINGIT e No Drawing. Application June 26, 1940,

Serial No. 342,448-

11 Claims.

This application is a continuation-impart of an application for U. S.Letters Patent filed by us March 4, 1940 under Serial No. 322,107, en-'titled Metallurgical flux and method of producing it, and like itrelates to the production of a synthetic fiux for use inmetallurgical'processes requiring a fluorspar-bearing fiux havingcertain more or less specific physical and chemical characteristics, asin the production of steel in open hearth furnaces or the like.

Fluorspar fluxes are used in steel manufacture and other metallurgicaloperations principally to insure the desired fluidity in the slag andthereby assist in refining the bath of molten metal but v withoutchanging the basicity or acidity of the slag, and it has been customaryto employ for this purpose fluorspar which occurs in nature in limitedquantities in certain parts of the United States, since not all naturalfluorspar ores possess the degree of purity and physical characteristicsrequisite for the purpose. For attainment of the best results incommercial practice, a fluorspar fiux usually should contain not lessthan 85% calcium fluoride (CaFz) and not more than 5% silica (SiOz) andalso, even when conforming to or excelling these chemical standards,must be available in quantity and preferably in a physical form suchthat thelargest pieces do not exceed in slzefa oneinch cube and theportion of the material which can be passed through a twenty-mesh screendoes not exceed 25% by weight of the total, but of course it ispreferable that the pieces be more uniform in size than is the case whenconsider- 5 able numbers of them approximate these maximum and minimumdimensions.

Much of the fluorspar used for fiuxing is derived from deposits offluorspar ore in the southern Illinois-Kentucky district, the ore beingcommonly either in the form of loose to partly coherent coarse gravelassociated with clay and lying near the surface or else in veins inassociation with. shale, limestone and silica and lying at greater depthbut in either case the ore can be concentrated to the requisite degreeof purity.

This concentration, however, is generally accomplished through logwashing and/or jigging operations which are wasteful in that substantiallosses occur in middling products and in the fine sizes so that it hasbeen distinctly preferable,

when possible, to obtain the ore for the production of metallurgicalfiux from a deposit in which it occurs naturally in a relatively purestate. As a result, but a limited number of the known fluorspar depositshave been practically available for flux production, as those in whichthe spar does not occur naturally in quantity with the requisite purityor with the essential physical characteristics are not satisfactory forthe purpose. 5 To the end thatindustry may be freed from its presentdependence for its requirements upon the limited output of thosedistricts in which there occur natural deposits of fluorspar suitable Ifor use as metallurgical fluxes, it is a principal object of ourinvention to provide a synthetic metallurgical fiux of the requiredfluorspar content as well as physical form produced from fluorsparconcentrates or other finely divided fluorspar-bearing materials. 15

A further object of the invention is the production of a metallurgicalflux from such materials in which the particles are agglomerated inlumps or pellets having adequate physical strength and resistance toabrasion and impact,

which are readily susceptible of incorporation in the slag, and whichare of sufficient mass individually to prevent their being carried outthe stack of an open hearth furnace by the draft.

A still further object is to provide a novel 25 method of producing fromfinely divided fluorspar flotation concentrate or similar substantiallypulverized fluorspar-bearing material a practical syntheticmetallurgical fluorspar flux of such character, physical condition andchemical 3O purity that it may be satisfactorily employed in place ofthe best grade of the natural product.

As is well known by those familiar withthe art, relatively finelydivided fluorspar such as that resulting from flotation concentration offluorspar ores and commonly known as fluorspar concentrate, in which theparticles are usually of the order of mesh, cannot be used as metallurgical flux for the reason that the spar particles are blown outthrough the furnace stack 40 by the violent currents of air and gases inopen hearth and other metallurgical furnaces before they can unite withor become incorporated in the slag layer floating on the bath of moltenmetal. To obviate this condition, it has been pro-posed to agglomeratespar concentrate with a tarry or other carbonaceous viscous binder andpress the mixture in molds to form briquettes large enough to preventtheir being blown out the stack when charged into the furnace. Thisexpedient is unsatisfactory, however, for the reason that the intenseheat of the furnace causes violent and rapid oxidation or combustion ofthe carbonaceous binder so that the briquettes virtually explode as soonas they are charged into it which is not only dangerous to theoperatives but causes wide dissipation of the spar particles containedin the.

briquettes, so that a large proportion of them is lost in the stackgases just as when loose concentrates are used.

Portland cement"ha's also been suggested for use as a binder inthemanufacture of fluorspar concentrate briquettes as it is cheap andnoncombustible but such briquettes do not have adequate strength andhardness to withstand the abrasion to which they are subjected duringhandling and shipment unless so much cement is used that the fluorsparcontent is diluted to an excessive degree. Sodium silicate and similarlywater soluble materials have also been utilized in briquettes but are sosusceptible to the action of rain and atmospheric moisture that thebriquettes cannot be economically stored and/or shipped and. suchbinders are therefore generally considered unsuitable for practical usein this connection.

These and other objections to the artificial fluorspar fluxes hithertoproposed are entirely obviated by our invention by means of which we areable to produce from fluorspar flotation concentrate or other finelydivided fluorspar, a fluorsparcontaining material in which the fluorsparparticles are held together in relatively hard lumps of suitable sizewhich can be handled and shipped without becoming pulverized orotherwise disintegrating, which do not readily dissolve in atmosphericmoisture or in other ways lose their normal physical and chemicalcharacteristics, and which, when charged into the furnace, do not burnwith undue rapidity or pass up the stack and thereby nullify in whole orin material part the desired effect of the fluorspar.-

As illustrative of the practice of our invention we shall initiallyrefer to the production in accordance therewith of a fluorspar fluxusing as an ingredient fiuorspar flotation-concentrate consistingprincipally, if not entirely, of particles of the order of one hundredmesh and finer, this being the size of the particles of the fluorsparflotation concentrates of relatively high purity now being produced incertain parts of the United States, particularly in the Rosiclaredistrict in Illinois. Such concentrate usually contains about 8% to 12%moisture whendelivered from the filter or comparable mechanism in theflotation circuit and in accordance with our invention may be usedimmediately in this condition without drying but it is preferable toascertain fairly accurately the percentage of moisture it contains so asto afford a basis for its dry weight measurement which is the basis onwhich the several ingredients of the flux are compounded. Thus we mixwith 100 parts of the fiuorspar concentrate by dry weight about threeparts more or less of a resinous vegetable oil product, preferably onesuch as that generally known as tall oil or talloel, sometimes known asliquid rosin. The oily or resinous fluid'so designated is produced incommercial quantities in the United States and abroad as a by-product ofmanufacture of paper from pine wood and while analytical chemistry ofthe higher fatty acids is not yet sufficiently developed to permitunqualified statements concerning its exact composition, it is said tocontain three classes of compounds, (a) rosin acids, (b) fatty acids and(c) non-acids such as sterols, higher alcohols and other unsaponiilablematter. This classification, however, is by some considered misleadingas it may suggest to chemists conclusions not home out in practice andthe material which we prefer to employ in carrying out our invention maytherefore perhaps best be identified as that now being sold on thedomestic market by the Industrial Chemical Sales Company of New York,Chicago and Cleveland under the trade name Liqro."

This substance is understood to contain about 45.8% rosin acids, 46.1%fatty acids and about 8.1% sterols etc., with but negligible moisturecontent of usually not more than a small fraction of 1% and ash residueon combustion as well as sulfur content likewise so-insigniflcant inquantity that they may be disregarded insofar as their effect upon thepractice of our invention is concerned.

The fluorspar concentrate is thoroughly mixed with the Liqro or acomparable material in either a continuous or in a batch machine and themixture sufficiently worked to form a plastic mass of substantiallyuniform consistency. This mass is then transferred to a machine adaptedto form it into pellets which machine may comprise, essentially, a plateor die perforated with a plurality of holes, which may be circular,square or of any other desired shape, and preferably about in greatesttransverse dimension, over one face of which heavy rollers are arrangedto travel so as to force the plastic material through the holes as it isdeposited on the plate and extrude it from its other face. A rotatingblade cooperative with the latter may be provided to sever the materialinto pellets of suitable length, desirably some to as it is extrudedthrough the holes by the pressure exerted by the rollers, or theextruded material may be allowed to simply break off by its own weightand thus form longer pieces usually some 3" in length which in thesubsequent drying and handling tend to break up into shorter pieces. Thepellets in either case are of sufiicient strength to at leasttemporarily .retain their shape.

The pellets are next dried to remove moisture carried into the mixturethrough the use of damp concentrate or otherwise, and after the dryingthe pellets are relatively hard and solid, substantially waterproof, andof sufficient strength and density for use for any purpose for which thebest grades of natural fluorspar flux are adapted.

The drying may be performed in any convend ient way and at anytemperature though it is preferable the latter be insumcient topartially oxidize the Liqro in the composition. Thus the pellets may bedried at atmospheric temperature, say 70 F., by merely exposing them tothe air, as on a drying table, or they may be dried in suitable furnacesor the like with equally good results at temperatures running up toaround 400 F. and of course in a much shorter time.

As exemplifying various temperature-time relations we have used fordrying the pellets, we have found they may be satisfactorily dried at 70F. in a period of 70 hours; at 180 F. in a period of two hours; at 276F. in a period of one-half hour, their attainment of constant weightafter exposure to these various temperatures for the approximate timesstated demonproduction the longer times required for drying the pelletsat the lower temperatures are not desirable from the standpoints ofeconomy and efliciency, and we therefore prefer to dry them in such away as to shorten the drying time to a half hour or thereabouts. Thiscan be readily efiected by discharging the moist pellets from thepelleting machine onto a moving belt arranged to convey them into asuitable oven where they are heated for the requisite period, forexample, about one-half hour at an oven temperature of 276 F. orthereabouts; while a higher temperature and shorter time might of coursebe employed, we prefer approximately the temperaturetime relationstated, as it is insufiicient to effectthe undesirable oxidation of the"Liqro to which we have referred although it may perhaps, similarly todrying at any temperature, result in volatilization of some of itslighter constituents. After removal from the furnace and cooling, thepellets are in condition for use without further treatment.

The Liqro remaining in the flux, being composed substantiallyexclusively of organic materials decomposes completely and passes outthe stack when the flux pellets are subjected to the heat of ametallurgical furnace and it' therefore has no appreciable metallurgicaleifect whatever upon the slag into which the flux is introduced or uponthe metal bath itself. The spar concentrate thus constitutes the onlyingredient of our flux which produces any noticeable metallurgi calresults in the furnace and its use therefore does not requirecompensation for other metallurgically active components. One of theseis of course sulfur, and we have suggested that Liqro, and hence ourflux, may contain some of it but not more than a small fraction of 1% ofthis element is likely or should be permitted to be present in Liqro,and as the Liqro constitutes only about 3% ofthe weight of the fluxpellets, and some sulfur may be lost in the drying operation, the sulfurcontent of the finished flux obviously cannot under ordinary conditionsamount to more than a very few hundredths of 1% and is usually evenless. Since metallurgical processes commonly require only a few poundsof flux per ton of charged metal it is evident that the quantity ofsulfur which could get into the metal from losses of it almost certainto occur through combustion or by inclusion in the slag.

While we have herein described with considerable particularity apreferred method of making our novel flux, we do not thereby desire orintend to restrict or confine ourselves specifically thereto as changesand modifications in the practice of the invention as well as in thematerials utilized will readily occur to those skilled in the art andmay be made if desired without departing from the spirit and scope ofthe invention as defined in the appended claims. c Having thus describedour invention, we claim and desire to protect by'Letters Patent of theUnited States:

1. A=metallurgical flux composed of separate, relatively hard,water-resistant pellets each coinprising finely dlvidedfiuorspar-agglomerated with this source is infinitesimal, evendisregarding heating the the residue-resulting from drying a mixture ofthe fluorspar and tall oil.

2. A metallurgical fiux composed of separate, relatively hard, waterresistant pellets each comprising the dehydration residue of a mixtureof finely divided fluorspar and tall oil.

3. A metallurgical fiux composed of individual pellets, each comprisinga dried mixture of finely divided fluorspar and tall oil.

- 4. A metallurgical flux composed of individual pellets, eachcomprising a dried mixture of fluorspar concentrate and tall oil in dryweight proportion of about 100 parts of the concentrate and about 3parts of the oil.

5. The method of making a synthetic fluorspar flux which comprisesmixing finely divided fluorspar with tall oil, forming the mixture intopel-' lets, and drying the pellets to thereby solidify and harden them.

6. The method of making a synthetic fluorspar flux which comprisesmixing finely divided fluorspar with tall oil in dry weight proportionsof about 3 parts of the oil to 100 parts of the fluorspar, forming themixture into pellets, and drying the pellets to thereby solidify andharden them.

7. The method of making a synthetic fluorspar fluxv which comprisesmixing fluorspar concentrate with tall oil in dry weight proportions ofabout 3 parts of the oil to 100 parts of the concentrate'to form aplastic mass, progressively forming the massinto individual pellets,dehydrating the pellets at a temperature insufiicient to aplets adaptedfor charging into a metallurgical furnace.

9. A metallurgical fiux in the form of individual pellets eachcomprising a plurality of particles of fluorspar flotation concentrateand, binding the particles .to each other, the residue remaining afterheating tall oil to approximately 200 F. to 400 F. in contact with theparticles.

10. The method of making a synthetic fluorspar flux which comprisesmixing fluorspar concentrate with tall oil in dry weight proportions ofabout 3 parts of the oil to 100 parts of fluorspar, forming the plasticmixture into pellets, and pellets'to approximately 200 F. to 400 F. tothereby solidify-and harden them.

11. The method of making a synthetic fluorspar flux which comprisesmixing fluorspar particles with tall oil in dry weight proportions ofabout 3 parts of the oil to 100 parts of fluorspar to form a plasticmass, progressively reducing the mass to rod-like form, severing therods to create pellets, heating the pellets to a temperature below about400 F. to thereby substantially dehydrate them and extract volatileconstituents,

and finally cooling the pellets to set and harden them.

FREDERICK C. ABBO'I'I'. CARL O.- ANDERSON.

